This invention relates to devices for testing whether an anchored member can resist a selected tension load. The present invention is especially useful in testing whether a retrofit anchor bolt embedded into a pre-existing concrete cementitious member is sufficiently secure to resist being pulled from the cementitious member when a selected tension load is applied. The present invention comprises both the device itself and the method of using the device.
In the light building industry, a number of different methods are used for checking the integrity of a bolt embedded in a cementitious member.
The most obvious method is, of course, to actually test an embedded anchor bolt's resistance to being pulled out of a cementitious member. Portable load cylinders have been developed to test the connection between anchor bolts and the cementitious member in which they are embedded. However, load cylinders are expensive to maintain and transport to a job site, and the actual testing of the bolts can be time consuming. Because the use of load cylinders is expensive, usually only a selected number of bolts are tested rather than all the bolts. The present invention improves upon this method by applying a tensile load to the bolt without the use of an expensive load cylinder.
Because the actual testing of bolts has been so expensive and time consuming, another alternative of checking the integrity of retrofit anchor bolts has developed. In this method, the integrity of the anchor bolt-cementitious member connection is safeguarded by having an inspector make sure that code-accepted practice for preparing a cementitious member or retrofitting bolts in a cementitious member is followed by actually having him observe the process. Again, this can be considered to be wasteful of time, especially if the inspector is not available to observe the process when it is convenient for the builder, such that the builder has to wait for the inspector.
Outside of the light building trade, a number of methods have developed for testing bolt connections that rely on relatively simple mechanical devices. These devices are found in heavy construction, mining and automobile building where bolt connections are critical. These devices usually consist of compression washer and nut combinations that can be used to measure the pull-out loads applied to a bolt, or alternatively the compression forces generated between a structural member that receives and anchors a threaded bolt and a nut threaded onto the bolt.
Most of these simple devices work along similar principles. A bolt having a threaded end is anchored in a structural member. The bolt is either held or anchored in such a manner that it cannot rotate with respect to the structural member. The threads on the bolt extend from the end of the bolt and past a bearing surface that is either part of the structural member that anchors the bolt or is in unyielding contact with the structural member. The load-indicating device is slipped over the threaded end of the bolt so that it is disposed against the bearing surface. A nut is then threaded onto the bolt, and tightened down so that it comes into contact with the load indicating device. After the nut comes into contact with the load-indicating device, torque is continuously applied to the nut until, hopefully, a designed-for failure of the load-indicating device occurs. Applying torque to the nut causes it to compress the load-indicating device between itself and the bearing surface. This creates an equal but opposite tension force between the bolt and the structural member anchoring it, testing that connection.
The load indicating device is designed to fail under a selected compressive force. Generally, the load-indicating device is selected to fail before the other members, but at a point where a meaningful load has been applied that tests the strength of the bolt and the strength of the connection between the bolt and the structural member.
Failure of the load-indicating device is indicated in a variety of fashions, and many devices are designed to fail once at a given load, but then be able to perform well beyond that load for the life-time of the connection. These particular devices are designed to be left in place after the connection has been tested. Other devices are used to measure whether a selected load on the bolt exceeds a given value.
Simple mechanical devices include washers having raised protuberances which are compressed back into the body of the washer under a given load. Other such members have a weakened intermediary portion between two main portions, the intermediary portion failing and allowing the two main portions to then bear on each other without similar failure at well beyond the first load. Other devices use washers that are broken between cooperating dies and punches. Other devices bend intermediate washer rather than break them. Some such devices are even designed to provide an indication when the selected load is removed from the load indicating device.
The device of the present invention differs from the devices of the prior art of which the inventor is aware by providing a tamper resistant method of proving that a bolt has been tested at a given load, without having to maintain the load on the bolt.